Abstract
Additive manufacturing (AM) of scaffolds enables the fabrication of customized patient-specific implants for tissue regeneration. Scaffold customization does not involve only the macroscale shape of the final implant, but also their microscopic pore geometry and material properties, which are dependent on optimizable topology. A good match between the experimental data of AM scaffolds and the models is obtained when there is just a few millimetres at least in one direction. Here, we describe a methodology to perform finite element modelling on AM scaffolds for bone tissue regeneration with clinically relevant dimensions (i.e., volume > 1 cm3). The simulation used an equivalent cubic eight node finite elements mesh, and the materials properties were derived both empirically and numerically, from bulk material direct testing and simulated tests on scaffolds. The experimental validation was performed using poly(ethylene oxide terephthalate)-poly(butylene terephthalate) (PEOT/PBT) copolymers and 45 wt% nano hydroxyapatite fillers composites. By applying this methodology on three separate scaffold architectures with volumes larger than 1 cm3, the simulations overestimated the scaffold performance, resulting in 150–290% stiffer than average values obtained in the validation tests. The results mismatch highlighted the relevance of the lack of printing accuracy that is characteristic of the additive manufacturing process. Accordingly, a sensitivity analysis was performed on nine detected uncertainty sources, studying their influence. After the definition of acceptable execution tolerances and reliability levels, a design factor was defined to calibrate the methodology under expectable and conservative scenarios.
Highlights
The stress is calculated as the force to be applied in order to obtain a certain displacement of the upper plane divided by the cross-sectional area of the scaffold (π·φ2/4 = 4π mm2), where φ is the diameter of the cylindrical scaffold
It is noteworthy to remark the differences between the stresses in the stress–strain relationship (Figure 12a) and those depicted in the finite element modelling (FEM) (Figure 12b)
Comparing the results of finite element modelling to the bone scaffold compression tests according to considered methodology, and once the uncertainty sources derived from manufacturing process are analysed during discussion, the following conclusions can be summarized: A methodology to perform FEM of 3D-printed bone scaffolds of any initial bulk material properties and geometry is defined
Summary
Human bones can be composed of high amounts of inorganics by volume, typically ranging from 50–60% up to 80–90% for some highly mineralized tissues, but always keeping some space for organics [1]. One of the most promising consists of the additive manufacturing of a temporary structure known as promising consists of the additive manufacturing of a temporary structure known as a “scaffold”, suitable for cell growth, with required porosity to stimulate osteogenesis, as a “scaffold”, suitable for cell growth, with required porosity to stimulate osteogenesis, as stated by Jakus et al [4], Karageorgiou and Kaplan [5] and Hutmacher [6]. The geometry and porosity of the fabricated scaffolds play an important role in the final mechanical properties of the implant [16,17]
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